1. Field of the Invention
This invention relates to novel acrylic fibers having high fire retardancy, and outstanding glossiness and transparency which are not lost even if they are dyed.
2. Description of the Prior Art
Modacrylic fibers, which are prepared from a copolymer containing a relatively large proportion of a vinyl halide, have a certain degree of fire retardancy. There is, however, a sharply increasing social demand for fibers having a higher degree of fire retardancy. Various methods are known for imparting fire retardancy to fibers, for example, employing a copolymer containing a fire retardant monomer, incorporating a fire retardant additive into the spinning solution, or applying a fire retardant agent to fibers during their posttreatment. The incorporation of a fire retardant additive into the spinning solution is most popular, since it imparts semipermanent fire retardancy to fibers without impairing their physical properties substantially.
Various substances are employed as the fire retardant additive, and include, for example, a halide such as a chloride or bromide, a nitrogen or phosphorus compound, and a metal compound. Few of these substances are effective for making acrylic fibers fire retardant, and though some of them are effective, it is necessary to employ a considerably large quantity. For example, halogen compounds such as paraffin chloride, diphenyl decachloride, tetrabromobutane and tetrabromophthalic anhydride, or phosphorus compounds such as bis(dibromopropyl)phosphate, dibromopropyl phosphate, and tris(bromochloropropyl)phosphate are effective, but it is not possible to obtain satisfactory results unless at least 25% by weight of any of them is employed relative to the resin from which fibers are prepared. The use of any such large quantity of the additive is impractical, since it is not only uneconomical, but also has an adverse effect on the mechanical, thermal and optical properties of the fibers.
It is well known that a metal compound, such as diantimony trioxide, antimonic acid, magnesium oxide or hydroxide, tin oxide or stannic acid, improves the fire retardancy of a halogen-containing high molecular substance if a maximum of 10% by weight thereof is added thereto. Any such inorganic compound is, however, insoluble in a solvent used in the preparation of acrylic fibers, and deprives the fibers of their transparency. Moreover, such a compound is likely to increase in pressure, and block the spinning nozzles.